Method of making aluminum clad steel



Jan. 23, 1951 F. R. HENsEL 2,539,246

METHOD oF MAKING ALUMINUM CLAD STEEL Filed Oct.v'7, 1944 11 /lu//v//wr/M1,2 1g

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` TWINS/7E 30 (mwN/www0 28 .STEEL v 2297 vf/e i I 4 /ll/M//VVM l ZZ?(ama/vm 42 #LUM/NUM .8.45.5 ZOY SIL V51? STEEL 4 I N V EN TOR. franz j?.fc/'mel WMM Patented Jan. 23, 1951 METHOD OF MAKING ALUMINUM CLAD STEELFranz R. Hensel, Indianapolis, Ind., assigner to P. R.. Mallory & Co.,Inc., Indianapolis, Ind., l corporation of Delaware Application October7, 1944, Serial No. 557,703

2 Claims.

This invention relates to overlay metals of aluminum bonded to an irongroup metal, and particularly to aluminum-steel overlay metal and itsmanufacture, and to aluminum-lined bearings.

2 The silver layer may be deposited by conventional electroplatingmethods. A suitable method is the following:

Silver plating on steel An object of the present invention is to improve5 For an adherent plate of silver on steel sur- .alummum overlay metaland-the methods of ma?" face condition is of prime importance. The ideal111g 1li and t0 improve alummum lmed bearmgs' surface is a chemicallyclean mirror finish Other Objects f the invention Wm be apparent Toplate on a rolled steel surface from the description and claims.

In the drawings; m 1. Degrease 1n an organic solvent.

Figure 1 is a diagrammatic illustration of a 2 Electl'O-CleanaIlOdCallyprocess for making aluminum-steel overlay metal; A phosphateor silicate cleaner may be used,

Figure` 2 is a Sectional elevation illustrating such as Ano'dexn oruoakte #9011: another method of bonding aluminum to steel; p n

Figure 5 illustrates an aluminum lined bearing 3. Rinse, half shellembodying features of the present in- 4, sulfuric acid dip; vention. 10%acid by volume.

A number of methods of producing aluminum Time 1 minute, clad steel havebeen tried heretofore. One meth 5 Rinseod comprises dipping steel into abath of molten 5 Copper gash; aluminum. `This method results in only avery s ti thin superficial layer which adheres to the steel olucon ,d bythe formation of an iron-aluminum compound Fopper (f yam e-- "oz/gal"1'4-2'0 which is extremely brittle. Another method com- Pre s? mm Cyamde81'1 prises the rolling together 0f a thin aluminum To,assu,lm hydroxide4'55 foil and steel. Again the bonding action is based n'sodlum phfspha2 on the formation of the brittle iron-aluminum Copper modes' o compoundwhich win fracture in bending and Temperatur? F 17o-175 which has a verylow fatigue strength. It has Cflrrem denslty 45 A S-F also beensuggested that a layer of zinc be inter- Tlme "mmutes" 2 posed betweenthe aluminum and steel to avoid '7. Rinse the brittle iron-aluminumlayer. This layer does 8. Sodium cyanide dip: not prevent thebrittleness altogether and is char- 40 oz./ga1. acterized by low meltingpoint and low strength. 40 sec,

The present invention overcomes all the objec- 9, Silver strike: tionsof the prior methods and provides a strong, S 1 t. ductile fatigueresistant bond. This is accom- 40 ouslfn" .d rt 5 plished by providing asilver bonding layer be- Payer .cyam ed-grams per d1 er" tween thealuminum and steel. P tassium cyau e't 1 The preferred method of makingthe overlay To asslurl Car Ona e "0"-- 15 metal comprises bonding alayer of silver to the Cempeadure F- 90"95 steel surface and anotherlayer of silver to the Tllrren ensl y 0A' S'F' aluminum surface and thenbonding the layers me "Seconds" 20 together by heat and pressure. 10.Silver plate:

The preferred method of applying the silver to Soluti n the steel and tothe aluminum is electroplating Sg .d ,2 although other methods may alsobe enployed 5. T1 Lamy "i-*grams per' mer" .6 such as silver vapordeposition, pressur/e bonding Pot im assmm cyan de D2 or fusion bonding.It is essential/that the silver To asslurl carbonate "g"- 38 adheretightly to the steel 'and therefore the sur- Cempeadure C" 30 face ofthe steel must be carefully prepared to Hen ensl y 15 A' s' F' receivethe-silver layer by cleaning, sand blast- Brightener of thecarbondisulflde type may be ing, pickling and bright annealing ifnecessary.

used.

assegna .at this current density, silver will be deposited the rate oi'.0001" in 2.5 minutes. l

In the experimental work a plate .001" thick was deposited.

The aluminum must also be carefully cleaned and prepared to receive thesilver deposit by using tor instance the following method:

Silver plating on, aluminum En plating on aluminum the time required forancdimng and modification is dependent on the grade of aluminum and thenature of the alloy. The following flow sheet applies to pure aluminum.

i. Degrease with organic solvent. 23. Polish lightly with a mildabrasive. S. Etch in sodium cyanide:

solution- Sodium cyanide grams per liter-- 60 Time minutes l. Anodize:

Solution- Oxalic acid grams per liter-- 30 A. C. current:

Voltagel0 v. at startraised to 50 v. Timeminutes.

isn alkali metal carbonate-chromate may be used in anodizing.

5. Modify anodic iilm:

Solution- Sodium cyanide as above Time-5 minutes.

The modifying treatment may be either basic or acidic, using sodiumcyanide or a dilute solution of hydro-uoric acid.

6. Rinse. 7. Nickel plate:

Sclution: (Watts type) Nickel sulfate grams per liter-- 330 Nickelchloride do 30 Boric acid do 30 Hydrogen peroxide to prevent gassing.

Temperature F 140 Current density 25-50 A. S. F.

At 25 A. S. F., nickel will be deposited at the rate of .0001 in 5minutes. An .0002 plate Was deposited.

Any type of nickel bath may be used.

8. Rinse.

9. Sodium cyanide dip.

10. Silver strike-as in steel. 11. Silver plate-as in steel.

a sufficiently high pressure is applied. It can be stated that thisphenomenon is a matter of cold welding. This is entirely different fromthe usual methods of pressure bonding where it becomes necessary to heatthe parts close to their melting points. This type of cold welding isparticularly useful in this invention where the cladding material isaluminum having a low melting point. Metals such as copper areundesirable because pressure bonding could only be accomplished attemperatures which are considerably above the melting of the aluminum orthe aluminum alloy.

Referring to Figure 1 a process of making silver-steel overlay metal isillustrated diagrammatically. A strip of steel sheet Il is unwound fromroll i4 and passes through a cleaning and electroplating apparatus I5which applies a layer of silver to one surface of the steel strip. Analuminum strip E0 is simultaneously unwound from roll ii and passesthrough a cleaning and electroplating apparatus i2 to apply a layer ofsilver to one surface. The two silver plated strips l0 and i3 are thenbrought together with the silver plated faces in contact and led througha hydrogen furnace it which heats them to pressure bonding temperaturein a hydrogen atmosphere. The contiguous strips emerge from the furnacethrough a hydrogen chamber ill and then pass between pressure rolls i3and i9 which apply suiiicient pressure to bond the silver surfacestogether thus completing the bimetal strip 20 which emerges from theprocess.

According to another method of carrying out the bonding process thesilver coated sheets oi aluminum and steel are placed between pressureplates of a hydraulic press while being simultaneously heated in areducing atmosphere. Figure 2 shows an arrangement suitable for thismethod comprising pressure plates 2l and 22 of a hydraulic press betweenwhich is interposed a stack comprising the following elements: iirst aTransite plate 23 against pressure plate 22 carrying an induction coil24 disposed in suitable groovings in the plate. Above the Transite plateare stacked a carbon plate 25, the aluminum sheet 26 coated with silverlayer 2l. steel plate 28 coated with silver layer 29 in contact withsilver layer 21, carbon plate 30 and upper Transita plate 3l, grooved tocarry induction coil 32. A hood 33 operating in a sand'seal 30 enclosesthe stack and permits the assembly to be enveloped in hydrogen. Highfrequency currents through induction coils 24 and 32 heat up the carbonplates 25 and 30 and the aluminum and steel layers until the pressurebonding temperature is reached. Pressure is applied eithersimultaneously or subsequently by pressure plates 2l and 22 to completethe bond between the two silver surfaces. If relatively thick aluminumand steel layers are used, the bonded slab may subsequently be rolleddown to a suitable thickness for the use contemplated.

In some cases the carbon plates 25 and 30 may be eliminated in theassembly described and the aluminum and steel plates heated directly bythe induction coils. The plates may also be heated by a hydrogen flameor by substituting heating coils for the induction coils 24 and 32. Inthis case the heating coils are mounted as closely to the aluminum andsteel plates as possible.

Another suitable method consists in stacking a number of bimetalassemblies on top of each other into a furnace operating in anon-oxidizing atmosphere. Hydraulic or mechanical means are provided tomove the bottom of the furnace against the bimetal stacks therebyexerting sufficient pressure to cause cold welding of the silver facesto each other.

It is sometimes desirable, especially where subsequent reductions are tobe made, to place the aluminum slab into a recess 'in the steel. Therecess may be formed by a machining operation or by use of apre'rolledsteel section such as a U or I section. The steel recess may beelectroplated with silver or coated with silver has been carefullycleaned and coated with silver and then placed in the recess after whichthe assembly is heated and rolled in a reducing atmosphere to completethe bond.

If the side walls of the steel section are tightly crimped over thecoated aluminum to force the latter into intimate contact with thecoated steel, it will not always be necessary to roll the assembly in areducing atmosphere as sumcient pressure will be maintained between thesurfaces to substantially exclude oxidizing gases prior to bonding. Thehigher expansion coemcient of aluminum also promotes a tight joint.

Figure 3 shows a steel U section 36 lined with a silver layer 36 andenclosing a slab of aluminum 3l to be bonded to the silver plated steelsurface. The edges lof the steel are crimped over at 38 to substantiallyseal the joint preparatory to rolling.

Figure 4 shows an assembly using a steel I section 39 both grooves ofwhich are plated with silver layers 40 after which aluminum slabs Il areinserted and the edges 42 of the steel :langes are turned over on top ofthe aluminum slabs.

After bonding, the assemblies are rolled down to the desired thickness,the flanges on the steel members preventing the spreading of the moreplastic aluminum during rolling and thus maintaining the same ratio ofaluminum to steel as the overall thickness is reduced.

While the thickness of the silver bonding layers may vary considerably,it is preferred for most applications that the total thickness of silverbetween the aluminum and steel amount to between .0003 to .006". Thuswhere both the aluminum and steel surfaces are plated with silver priorto bonding, each layer of silver may be within the range .00015 to .003.If the bonded overlay metal is subsequently reduced by rolling, thethickness of the silver layer will of course also be reduced in thenished bimetal.

Silver offers several advantages in the making of aluminum-steel overlaymetals as described herein. The silver bonds readily to both aluminumand steel and while the metallurgical characteristics of this excellentbond are not completely understood, it is believed that the bondsconsist of a combination of ilne silver, silveraluminum alloys andsilver-iron alloys. Since silver welds readily to itself at relativelylow temperatures such as 350 to 500 C. the bonding can be producedwithout the detrimental eiects of overheating the aluminum.

Various steels may be used in forming the overlay metal such as ductilecarbon or alloy steels in addition to low carbon steel. Commercialaluminum or aluminum base alloys may be used for the aluminum component.

y Austenitic steels such as nickel, nickel manganese, nickel chromiumcompositions may also be used having a coefllcient of expansion matchingthe coeflicient of the aluminum or aluminum alloy, or in some cases thesteel may be selected to match the coefcient of the silver layer. s Inplace of steel, ductile nickel and cobalt base alloys may be used, suchas Monel'metal, and the standard nickel-manganese alloys, such as A, B,C and D nickel.

Figure 5 shows another embodiment of the invention wherein a case andsilver coated aluminum alloy bearing lining half shell 43 is pressedinto a silver coated half shell backing M. The lining is bonded to thebacking by simultaneously applying heat and pressure between suitablyformed dies in a reducing atmosphere. The two silver coatings weldtogether into a single bonding layer 45.

The term aluminum in the claims is intended to include aluminum basealloys.

While speciilc embodiments of the invention have been described, it isintended to cover the invention broadly within the spirit and scope ofthe appended claims.

What is claimed is:

1. The continuous method of making aluminum-steel overlay metal fromlayers of aluminum and steel which comprises cleaning the bondingsurfaces oi the aluminum and steel layers, coating the cleaned surfacesof both said layers with layers of silver having thicknesses not over.003, placing said layers of aluminum and steel together with the silvercoatings in contact, preheating the layers in a non-oxidizing atmosphereto a temperature below the melting point of silver and between about 350and about 500 C., and hot rolling said preheated layers to reduce thethickness of the layers and to permanently bond the layers together.

2. Ihe continuous method of making an aluminum-lined steel-backedbearing which comprises cleaning the bonding surfacesl of an aluminumlining and of a steel backing layer, passing the said layers throughindividual silver plating baths to deposit thereon coatings of silverhaving thicknesses not over .003", placing said layers together with thesilver coatings in contact, preheating the layers in a nonoxidizingatmosphere to a temperature below the melting point of silver andbetween about 350 and y500 C., and hot rolling said preheated layers toreduce the thickness of the layers and to permanently bond the layerstogether.

FRANZ R. HENSEL.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 625,117 Martin May 16, 1899673,126 Martin Apr. 30, 1901 685,758 Griffith Nov. 5, 1901 757,852Wachwitz Apr. 19, 1904 894,163 Monnot July 21, 1908 894,164 Monnot July21, 1908 909,924 Monnot Jan. 19, 1909 929,778 Monnot Aug. 3, 19091,156,169 Monnot Oct. 12, 1915 1,554,097 Jordan Sept. 15, 1925 1,731,790Payne Oct. 15, 1929 1,792,377 Jordan Feb. 10, 1931 1,850,997 AssmannMar. 29, 1932 2,094,483 Weder Sept. 28, 1937 2,171,040 Merritt Aug. 29,1939 2,266,276 Schluchter Dec. 16, 1941 2,266,319 Hobbs Dec. 16, 19412,269,523 Deutsch Jan. 13, 1942 2,277,023 Steiner Nov. 17, 19422,289,572 Underwood July 14, 1942 2,294,404 Hensel Sept. 1, 1942 (Otherreferences on following page) Number Number Great Britain May 7, 1942OTHER REFERENCEB- P. 130. Aviation. Jan. 1927. pub. by the Gardner Pub.Co., Inc. Copy in- Aviation, voi. 22, Library P.O. T1, 501,' A8.

Pp. 188, 189, 271, 272, Silver in Industry (1940) by Lawrence Addicks,Reinhold Pub. Corp., 330 West 42nd St., New York, N.Y. (Copy in Div.14.)

1. THE CONTINUOUS METHOD OF MAKING ALUMINUM-STEEL OVERLAY METAL FROMLAYERS OF ALUMINUM AND STEEL WHICH COMPRISES CLEANING THE BONDINGSURFACES OF THE ALUMIUM AND STEEL LAYERS, COATING THE CLEANED SURFACESOF BOTH SAID LAYERS WITH LAYERS OF SILVER HAVING THICKNESSES NOT OVER.003", PLACING SAID LAYERS OF ALUMINUM AND STEEL TOGETHER WITH THESILVER COATINGS IN CONTACT, PREHEATING THE LAYERS IN A NON-OXIDIZINGATMOSPHERE TO A TEMPERATURE BELOW THE MELTING POINT OF SILVER ANDBETWEEN ABOUT 350* AND ABOUT 500* C., AND HOT ROLLING SAID PREHEATEDLAYERS TO REDUCE THE THICKNESS OF THE LAYERS AND TO PERMANENTLY BOND THELAYERS TOGETHER.